As a general rule, no. The "distribution statement" on US government documents has to do with sensitive information, not copyright. For instance, in the Department of Defense, a document with a graph of velocity vs. distance for a new bullet might be marked "Distribution D - Critical Technology," meaning that the information shouldn't be given to anyone outside the DoD or a DoD contractor (the information might not be classified, but it's not something to go telling everyone about). A slide that talks about what the lab did that year and has a bullet point for "Invented new, longer-ranged bullet" might be marked "Distribution A," meaning that there's no issue with telling everyone that the lab invented a new bullet with a longer range.
Any work produced by an officer or employee of the United States Government as part of their official duties is not protected under US copyright law. A work produced by someone else (like a contractor) likely is protected. There are plenty of public-domain documents that are not approved for public release, and there are plenty of copyrighted documents that can be publicly released. The Department of Energy has many contractor-operated labs, and it appears that the document you gave was written by a contractor, meaning that copyright would generically apply.
That doesn't necessarily mean that this document in particular, or the image in particular, is copyrightable. But it's not safe to assume that "public release" means "public domain," because they're different things entirely.